In the factory automation control and the Intranet measurement (LXI, LAN eXtension Instrument), the precise timing synchronization is important.
In the factory automation control (e.g., manufacturing apparatus automation control or robot arm automation control) emphasizing the precise timing synchronization, the motion control, such as robot arm control, motor rotating speed control or the like, requests the highest communication timing synchronization. The timing synchronization has to be reached between a grand master and nodes, such as a robot arm and a motor. If the timing synchronization is not precise, the product may fail, thereby directly affecting the profit and causing great loss of money.
The Intranet measurement may be adapted to various environments such as a vehicle automation test production line, an airplane electronic apparatus test and a rocket launching base. Among these environments, the timing synchronization has to be reached between multiple computers, multiple machines and multiple sensing members so that signals returned by multiple sensing members may be measured in a specific time period and the signals may be analyzed subsequently.
In prior network timing synchronization, each network node, such as a provider edge (PE) router, a customer edge (CE) router, a customer premise equipment (CPE) or a gateway, needs to support a precision time protocol (PTP) and a best master clock (BMC) algorithm.
FIG. 1A (Prior Art) shows the prior art timing synchronization. As shown in FIG. 1A, a CPE 10 and a CPE 16 execute the BMC algorithm to determine the master and the slave (assume the CPE 10 is the master and the CPE 16 is the slave). Thereafter, the CPE 10 transmits a timing synchronization request packet to the CPE 16 through a PE router 12 and a CE router 14 so that the CPE 16 is in timing synchronization with the CPE 10. In this associated technology, the mechanism is referred to as a “transmissive timing synchronization mechanism”. That is, the CPE 10 and the CPE 16 respectively pertain to different sub-networks, and the timing synchronization request packet needs to transmit through multiple sub-networks, such as the sub-network between the CPE 10 and the PE router 12, the sub-network between the PE router 12 and the CE router 14, and the sub-network between the CE router 14 and the CPE 16. Thus, the timing synchronization request packet has a transmission delay.
In addition, if the CPE 10, which is originally the grand master, is removed or crashed, the nodes 12 to 16 cannot receive the timing synchronization request outputted from the CPE 10. Thus, the nodes 12˜16 start to execute the BMC algorithm to determine which one should become a new grand master. Thus, the overall timing synchronization is disturbed. Taking the factory automation environment as an example, if the original grand master is removed or crashed, the timing information of the node (production line) is reset so that a failed product may be obtained.
FIG. 1B is a schematic illustration showing how the prior art adds a new node or a hack node. As shown in FIG. 1B, when a new CPE 18 is added, the new CPE 18 outputs the best timing synchronization request packet Ebest to all the nodes 10˜16 to request other nodes to be in timing synchronization with itself and to determine the master-slave relationship again. Because all the nodes need to execute the BMC again to determine a new master-slave relationship, the timing synchronization between all the nodes is disturbed. So, the overall timing synchronization is negatively influenced. More particularly, it is not allowed to disturb the timing information of other timing synchronized nodes in the factory automation environment, because a failed product may be obtained due to disturbance of the timing synchronization.
More particularly, if the new CPE 18 is a hack node, the hack node outputs the best timing synchronization request packet Ebest to nodes 10˜16 to force nodes 10˜16 to become the slave nodes and to make itself become the master node, thereby causing the problem in security.